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How do I just plain and simple get ride of voles, period?

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A

Voles are a rodent species capable of causing a lot of damage because of the their ability to multiply quickly in response to abundant food. Cultivated crops, orchards, and lawns in Utah often feel the burnt of this damage. The damage may be particularly severe in areas experiencing drought conditions.

Population levels generally peak every 2 to 5 years, but these cycles are not predictable. These populations shifts may result in densities ranging from a few to several hundred voles per acre. In rare cases, vole populations may become extremely dense. During the early 1900s, vole populations were estimated at 25,000 per acre in some areas of Nevada.

VOLE PROBLEMS

As I mentioned, voles can cause severe damage to orchards, ornamentals, and tree plantings by girdling seedlings and mature trees, especially when populations are high. Studies in New York have demonstrated that girdling by voles can reduce fruit yield in apple orchards by as much as 66%.

Girdling of woody plants primarily occurs during fall and winter. Field crops, lawns, and golf courses also may be damaged by vole’s extensive runway and tunnel systems.

Fortunately, voles pose no major public health problems because of infrequent contact with humans.

However, they can harbor disease organisms, such as plague and tularemia. For this reason, voles should never be handled. If you have to handle a vole, or any other species of wildlife, you should wear the appropriate protective clothing (e.g., leather gloves).

DAMAGE IDENTICATION

Girdling damage and gnaw marks caused by voles are similar to that of many other species of wildlife, particularly rabbits. This, coupled with vole’s small size and inconspicuous nature, often leads individuals to believe vole damage is caused by other wildlife species. Vole girdling is characterized by non-uniform gnaw marks which occur at various angles and in irregular patches. In contrast, rabbits clip branches with neat, clean cuts.

Additionally, gnaw marks left by voles characteristically are about 1/8 inch in width and 3/8 inch in length; gnaw marks caused by rabbits usually are larger than this.

Careful examination of girdling damage may be needed to identify the animal that caused damage.

However, perhaps the most prominent sign of vole damage is the presence of their extensive runway system. Runways are 1 to 2 inches in width and vegetation is often clipped close to the ground next to well-traveled routes.

CONTROL

Control usually falls into 3 categories - habitat modification, exclusion, and population reduction. To ensure long-term control all three measures should be implemented simultaneously.

Habitat Modification

The elimination of weeds, ground cover, and litter around lawns and ornamental plantings can reduce habitat suitability for voles and lead to a decreased likelihood of vole damage. For example, lawns should be mowed regularly and mulch should be cleared 3 feet or more from the base of trees. Additionally, soil cultivation destroys vole runway-systems and may kill voles outright. For these reasons, plots of annual plants often are less susceptible to vole damage than perennial plants.

Exclusion

Cylinders made of hardware cloth (available at most hardware stores) are often effective in excluding voles and protecting individual plants. The mesh size of the hardware cloth used to construct cylinders should be no larger than 1/4 inch in size. The cylinder should be buried at least 6 inches below the ground surface to ensure that voles will not burrow under the hardware cloth and gain access to the plant. Although this technique will protect individual plants, fencing typically is not effective in

3 protecting large areas (e.g., lawns) and probably is cost prohibitive.

There are two chemicals approved for use in By EPA for repelling voles. These two repellents may contain thiram (a

fungicide) or capsaicin (chemical that makes peppers

"hot") and act by altering the taste of plants and making them unpalatable to voles. Although these repellents may provide temporary protection for plants, their effectiveness usually is short-lived. Voles may become accustomed to such repellents and forage on plants even after treatment.

For a more long-term prevention effort, other techniques should be considered.

Population Reduction

The EPA also currently approves of two toxicants which may be used to lethally control vole populations. The toxicants are zinc phosphide and anticoagulants. Of these, zinc phosphide is more commonly used. Zinc phosphide

(2%) is available in pelleted and grain bait formulations and typically is broadcast at rates of 6 to 10 pounds per acre. Additionally, zinc phosphide baits may be placed by hand in runways and burrow openings. Occasionally, it may be necessary to prebait (placement of nontreated bait prior to applying toxic baits) an area where voles hive become shy of toxic baits. Although zinc phosphide baits can be highly effective in reducing vole populations, you should be aware that this chemical is also toxic to groundfeeding birds, particularly waterfowl. Hand-placing baits in burrows and runways greatly reduces the risk of birds feeding on zinc phosphide baits. Zinc phosphide is also toxic to humans when ingested and may be absorbed through the skin. For these reasons, you should always wear gloves when handling zinc phosphide baits and dispose of the gloves in a safe manner. Additionally, zinc phosphide baits should be kept away from small children.

Zinc phosphide is considered a restricted-use chemical. As such, to use zinc phosphide baits you must be a certified applicator. If you are interested in becoming a certified applicator, contact your local county extension office.

Anticoagulant baits are also an effective means of reducing vole populations. Anticoagulants often are used to reduce rodent populations in general; approximately 95% of mouse and rat control is performed with anticoagulants.

As with zinc phosphide baits, anticoagulants can be broadcast over an area or placed by hand in runways and burrows. Additionally, anticoagulant baits are often glued to the inside of a water repellent paper tube to make an effective, disposable bait container. Anticoagulants work much slower than zinc phosphide and death is delayed for several days following the ingestion of a lethal dose. This slow action offers an important safety advantage where pets or livestock frequent because it provides time to administer the antidote (Vitamin K1) to an affected animal.

Like zinc phosphide baits, anticoagulants can also be toxic to humans. Therefore, you should take precautions to prevent children from gaining access to anticoagulant baits.

For more information about these toxicants, their use, and how to obtain them, contact your local extension office.

THINGS NOT TO DO

Frightening devices have been shown to be ineffective in reducing vole damage.

Fumigants usually are not effective in controlling voles because the complexityand depth of vole runways and burrows allow the fumigant to escape before voles are exposed to it.

Trapping may be effective in controlling very small vole populations, but, because of vole’s high reproductive rate, the time and labor costs required to eliminate voles are probably prohibitive.

In the event that voles invade your house (which is a rare event), individuals can be removed with snap traps or live traps as you would for house mice. Shooting generally is not regarded as a desirable method of vole population control.

Posted on 1 Aug 2007

Terry Messmer
Professor & Wildlife Resource Specialist

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